1. Field of the Invention
The present invention relates to light valve image projection systems. More specifically, the present invention relates to techniques for illuminating multicolor light valve image projectors.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Much progress in the state of the art of high quality large screen projectors can be attributed to the development of the liquid crystal light valve. The reflective mode liquid crystal light valve is a thin film, multilayer structure comprising a liquid crystal layer, a dielectric mirror, a light blocking layer, and a photoresponsive layer. The multi-layer structure is sandwiched between two transparent electrodes. A polarized projection beam is directed through the liquid crystal layer to the dielectric mirror. An input image of low intensity light, such as that generated by a cathode ray tube, is applied to the photoresponsive layer. Application of low intensity light to the photoresponsive layer induces a spatial variation in the voltage drop across the photoresponsive layer in the pattern of the input image. The spatial variation in voltage drop across the photoresponsive layer is mirrored in reverse within the liquid crystal given the series relationship existing between the two layers. Linearly polarized projection light passing through the liquid crystal layer and reflecting from the dielectric mirrors is polarization-modulated in accordance with the input image impressed on the photoconductor and mirrored in the liquid crystal layer. Accordingly, the light valve is operative to create a replica of an image focused onto the photoconductive layer which can be projected with magnification to produce a high brightness image on a viewing screen. U.S. Pat. No. 4,019,807 issued to D. D. Boswell et al discloses such a high-performance reflective mode liquid crystal light valve.
A graphics display projector using a liquid crystal light valve of the above type is described in an article entitled "Application of the Liquid Crystal Light Valve to a Large Screen Graphics Display", published in the 1979 Society for Information Display (SID), International Symposium, Digest of Technical Papers, May 1979, pp. 22-23. More sophisticated liquid crystal light valve image projection systems are illustrated in the following U.S. Pat. Nos. 4,425,028, issued to R. J. Gagnon et al on Jan. 10, 1984; 4,544,237, issued to R. J. Gagnon on Oct. 1, 1985; 4,461,542 to R. J. Gagnon on July 24, 1984; and 4,464,019, issued to R. J. Gagnon on Aug. 7, 1984.
In many conventional liquid crystal light valve image projection systems, three primary color images (red, green and blue) are displayed in optical registration on a viewing screen. The three primary color images are typically generated by three separate light valves, which are projected on the screen by three separate projection lenses. The projection lenses are arranged about an optical axis which passes through the composite image displayed on the screen. In such an arrangement of projection lenses it is necessary that the three primary color images converge in the plane occupied by the screen. In order to effect such convergence, complicated and expensive optical arrangements with accompanying electronics are typically required.
In other light valve color projection systems the red, green and blue primary color images are generated by separate portions of a single light valve. However, in such single light valve systems each primary color image does not utilize the full resolution of the entire light valve. Accordingly, the full-color image projected by the single light valve may be of less than desired resolution.
As is well known, certain color projection systems utilize cathode ray tubes, rather than light valves, in order to generate the individual primary color images. In color projection systems having only a single cathode ray tube, the red, green, and blue primary color images may be generated by positioning a rotating filter wheel over the face of the cathode ray tube (CRT). For example, in certain early color televisions the filter wheel is oriented such that individual primary color images are sequentially projected to create a composite full-color projected image. Since the entire face of the CRT is employed in generating each sequential primary color image, the resolution of the composite image is higher than in systems wherein portions of a CRT are dedicated to continuously generating a single primary color image.
However, mechanical arrangements or other techniques for sequentially generating primary color images in single light valve projection systems are not heretofore known to exist. Moreover, high speed mechanical parts are typically sensitive to vibration and often require periodic adjustment. Accordingly, high speed parts such as filter wheels are disfavored for use in projection systems operative in rugged environments or in systems designed to require minimal maintenance.
Thus, a need in the art exists for a single light valve full-color projection system operative to generate a sequence of primary color images without the aid of high speed mechanical parts.